(679g) Ethanol Conversion to C4+ Olefins over Bimetallic Zn-, Cu-, Y-, and La-Containing Beta Zeolite Catalysts

The identification of catalytic pathways for generating renewable fuels and fuel additives from biomass-derived feedstocks is of critical importance to achieve carbon-neutral operations. Ethanol remains a primary renewable feedstock for synthesizing sustainable aviation fuels, yet it requires multiple C-C bond formation steps to generate favorable fuel precursors. Here, we present our latest work developing Lewis acidic catalysts consisting of multifunctional bimetallic Zn-Y/Beta, Cu-Y/Beta, and Cu-La/Beta zeolites for ethanol upgrading into C₄₊ olefins as precursors to jet-range hydrocarbons. This ethanol-to-olefins (ETO) pathway proceeds through an acetaldehyde intermediate and requires a complex network of dehydrogenation, aldol condensation, Meerwein–Ponndorf–Verley (MPV) reduction, dehydration, and hydrogenation to form mono-olefin species. This range of reactions can be accomplished over a single Lewis acidic bimetallic zeolite catalyst given the proper choice of metal active sites and reaction conditions. Zn, Cu, Y, and La active sites are probed via pyridine IR, XAS, and HAADF-STEM measurements to investigate bulk active site properties prior to correlating specific metal species to various reactions in the ETO network. The second metal heteroatom (e.g., Y, La) catalyzes the aldol condensation and dehydration reactivity where the choice of metal shifts the product selectivity from butene-rich streams to longer chain olefins such as hexenes and octenes. The Cu-La/Beta catalyst can achieve 43% selectivity to C₅₊ olefins at high ethanol conversion (98% conversion, 623 K, 73% C₄₊ selectivity, <4% C₁-C₃ hydrocarbons) compared to product distributions obtained over Cu-Y/Beta which show similar C₄₊ olefin selectivity at significantly higher butene selectivity. These Cu-La/Beta catalysts are a state-of-the-art catalyst for long-chain olefin formation as an intermediate for sustainable aviation fuel generation.